A major objective of the proposed research is to increase understanding of vocal communication systems, by investigating the vocalizations of free-ranging East African vervet monkeys, and comparing these with human communication. Our previous work has revealed striking similarities between the use of vocalizations by vervets and the simplest use of words by humans. One study will examine how vervets preceive vocal signals, and if they use complex sequences of calls under natural conditions. A second study will examine the acoustic properties of vervet vocalizations, allowing a comparison of vocal production in human and non-human primates. A third study will examine the ontogeny of vervet vocalizations, focusing especially on those areas in which the vervet's vocal development parallels the development of human speech. In each case, methods will include sound spectography and computer-aided acoustic analysis, plus observations, tape-recordings, and filmed playback experiments in the monkey's natural habitat. Comparison between human and non-human primate vocalizations, in both physical aspects of the acoustic signals, their perception, and the contexts of their production, can provide important information concerning human linguistic and 'paralinguistic' vocalizations. Comparative research on non-human primates cn lead to new diagnostic tests and theraputic techniques for humans, and is essential if we are to understand the neural control of different human communication systems.